A micro-channel device includes one or more micro (sub-millimeter) channels through which one or more small volumes of samples are routed for processing and/or analysis. An example of such a device includes a sample carrier such as a biochip, a lab-on-a-chip, and/or other micro-channel device. An application in which a micro-channel device has been used is DNA sequencing. DNA sequencing generally is a method for determining an order of nucleotide bases (adenine, guanine, cytosine, and thymine) of DNA in a sample of DNA.
For DNA sequencing, the DNA in the sample is lysed, producing fragments of sequences of the four nucleotides. The fragments are replicated through polymerase chain reaction (PCR) and labeled with target specific fluorescent dyes (e.g., one for each nucleotide base), each dye having a different spectral emission characteristic (e.g., wavelength, frequency, energy and color). The labeled fragments are separated by size through electrophoresis. The DNA fragments are sequenced based on the spectral characteristics of the dyes.
Such sequencing has included using an optical detection system to illuminate the fragments with an excitation signal and detect fluoresced radiation from the dyes of the fragments. The detected spectral information is used to identify the nucleotides and sequence the DNA. However, only about five percent (5%) of the excitation signal is absorbed by the dyes; the other ninety-five percent (95%) traverses the sample carrier and can produce background signal, stray light, and noise inside the optical system, which may be detected along with the fluoresced radiation, which may negatively impact DNA sequencing.
One approach to mitigating the above includes placing a mirror behind the sample carrier to direct excitation signal traversing the sample carrier towards a “black box” collector, where the signal is collected and trapped. FIG. 1 shows an example in which a portion 102 of an excitation signal 104 traversing a sample carrier 106 is directed by a mirror 108 to a collector 110. Emission 112 represents signal emitted by a sample (carried by the sample carrier 106) in response to absorbing the excitation signal 104. Unfortunately, the mirror 108 and the collector 110 consume space. For example, in one instance, the mirror 108 and the collector 110 collectively occupy a volume on the order of about two inches by two inches by a half an inch (2″×2″×0.5″). Furthermore, the mirror 108 and the collector 110 increase overall system cost. At least in view of the foregoing, there is an unresolved need for other approaches for mitigating the excitation signal traversing the sample carrier without being absorbed.